Explain the components and function of a UV-VIS spectrophotometer, list EM spectrum in decreasing energy order, and give 3 applications in chemical analysis.

Here are the solutions to the chemistry questions:

4. (a) Using a block diagram show the workings of a UV-VIS spectrophotometer.

[Light Source] --> [Monochromator] --> [Sample Cell] --> [Detector] --> [Amplifier] --> [Readout/Display]

• Light Source: Emits light across the UV and visible regions of the electromagnetic spectrum.
• Monochromator: Selects a specific wavelength of light to pass through the sample.
• Sample Cell: Holds the sample solution through which the monochromatic light passes.
• Detector: Measures the intensity of the light that has passed through the sample.
• Amplifier: Increases the signal from the detector.
• Readout/Display: Presents the absorbance or transmittance data.

4. (b) List the component radiations of the Electromagnetic Spectrum in the order of decreasing energy.

The component radiations of the Electromagnetic Spectrum in order of decreasing energy are:

• Gamma rays
• X-rays
• Ultraviolet (UV) radiation
• Visible light
• Infrared (IR) radiation
• Microwaves
• Radio waves

4. (c) Give three applications of the UV-VIS spectrophotometer in chemical analysis.

• Quantitative analysis of substances by determining their concentration in a solution.
• Qualitative analysis for identifying substances based on their unique absorption spectra.
• Monitoring reaction kinetics by measuring changes in absorbance over time.

5. (a) List the elements in the halogen group in the periodic table (Name and symbol).

The elements in the halogen group (Group 17) are:

• Fluorine ($\text{F}$)
• Chlorine ($\text{Cl}$)
• Bromine ($\text{Br}$)
• Iodine ($\text{I}$)
• Astatine ($\text{At}$)
• Tennessine ($\text{Ts}$)

5. (b) List the electronic configuration of the following elements and give two examples each of their applications: iodine, fluorine and chlorine.

• Iodine ($\text{I}$)

  • Electronic configuration: $[\text{Kr}] 4\text{d}^{10} 5\text{s}^2 5\text{p}^5$
  • Applications:
    • Used as an antiseptic (e.g., in tincture of iodine).
    • Essential for thyroid hormone production in the human body.

• Fluorine ($\text{F}$)

  • Electronic configuration: $[\text{He}] 2\text{s}^2 2\text{p}^5$
  • Applications:
    • Used in toothpaste and water fluoridation to prevent tooth decay.
    • Production of fluorocarbons (e.g., refrigerants, non-stick coatings like Teflon).

• Chlorine ($\text{Cl}$)

  • Electronic configuration: $[\text{Ne}] 3\text{s}^2 3\text{p}^5$
  • Applications:
    • Used for water purification and disinfection.
    • Production of PVC plastic and other organic compounds.

6. (a) List 5 transition elements: name and symbol.

Five transition elements are:

• Iron ($\text{Fe}$)
• Copper ($\text{Cu}$)
• Nickel ($\text{Ni}$)
• Zinc ($\text{Zn}$)
• Chromium ($\text{Cr}$)

6. (b) Give any three properties of transition elements.

• They typically form colored compounds due to d-d electron transitions.
• They exhibit variable oxidation states.
• They can act as catalysts in many chemical reactions.

6. (c) What are metal alloys and give the composition and uses of the following alloys: stainless steel, bronze and brass.

• Metal alloys: A metal alloy is a mixture of two or more elements, at least one of which is a metal, combined to achieve properties that are superior to those of the pure component metals.

• Stainless steel:

  • Composition: Primarily iron ($\text{Fe}$) with a minimum of 10.5% chromium ($\text{Cr}$), and often nickel ($\text{Ni}$), molybdenum ($\text{Mo}$), and carbon ($\text{C}$).
  • Uses: Cutlery, surgical instruments, kitchen sinks, architectural applications, and industrial equipment due to its corrosion resistance.

• Bronze:

  • Composition: Primarily copper ($\text{Cu}$), usually with tin ($\text{Sn}$) as the main additive, but sometimes with other elements like zinc, manganese, or aluminum.
  • Uses: Sculptures, bells, musical instruments, marine fittings, and bearings due to its strength and corrosion resistance.

• Brass:

  • Composition: Primarily copper ($\text{Cu}$) and zinc ($\text{Zn}$).
  • Uses: Decorative items, musical instruments, plumbing fixtures, electrical fittings, and ammunition casings due to its malleability, ductility, and acoustic properties.

7. (a) Define electronegativity.

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons towards itself in a chemical bond.

7. (b) Define ionisation energy.

Ionisation energy (or ionization energy) is the minimum energy required to remove one electron from a gaseous atom or ion in its ground state.

7. (c) Define paramagnetism.

Paramagnetism is a form of magnetism whereby some materials are weakly attracted to an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. This property arises from the presence of unpaired electrons in the atoms or molecules of the material.

7. (d) Define interstitial and substitution alloys.

• Interstitial alloys: Interstitial alloys are formed when small atoms (like hydrogen, carbon, or nitrogen) occupy the interstitial sites (spaces) within the crystal lattice of a larger metal atom. This typically increases the hardness and strength of the metal.

• Substitution alloys: Substitution alloys are formed when atoms of the solute metal replace atoms of the solvent metal in the crystal lattice. This occurs when the atoms of the two metals are of similar size and have similar chemical properties.